The hydrophilic domain of Tic110, an inner envelope membrane component of the chloroplastic protein translocation apparatus, faces the stromal compartment
The hydrophilic domain of Tic110, an inner envelope membrane component of the chloroplastic protein translocation apparatus, faces the stromal compartment
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DOI：
10.1074/jbc.273.26.16583
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发表时间：
1998-06-26
影响因子：
4.8
通讯作者：
Keegstra, K
中科院分区：
文献类型：
--
作者：
Jackson, DT;Froehlich, JE;Keegstra, K
以前已经发现，Tic110，叶绿体内被膜的一个完整的蛋白质，是叶绿体蛋白质输入装置的一个组成部分。然而，存在相互矛盾的报告，关于这种蛋白质的内包膜膜的拓扑结构。在这份报告中，我们提供的证据表明，大（>90 kDa）的Tic110的亲水结构域是本地化的叶绿体基质。胰蛋白酶是一种不能穿透内包膜的渗透屏障的蛋白酶，它既不降解Tic110也不降解暴露于基质区室的其他蛋白质，但能够消化暴露于两个包膜之间的膜间空间的蛋白质。以往的报道表明胰蛋白酶能够降解Tic110是受到蛋白酶活性不完全淬灭的影响，当胰蛋白酶没有被充分淬灭时，它能够消化Tic110，但只有在叶绿体破裂之后。因此，当胰蛋白酶用作分析工具时，有必要采用适当的淬灭方案，如本文所述。基于大部分的Tic110的基质定位，我们建议，这种蛋白质可能参与招募基质因子，可能分子伴侣，在蛋白质进口的易位装置。
It has previously been found that Tic110, an integral protein of the chloroplast inner envelope membrane, is a component of the chloroplastic protein import apparatus. However, conflicting reports exist concerning the topology of this protein within the inner envelope membrane. In this report, we provide,evidence that indicates that the large (>90-kDa) hydrophilic domain of Tic110 is localized within the chloroplast stroma. Trypsin, a protease that cannot penetrate the permeability barrier of the inner envelope membrane, degrades neither Tic110 nor other proteins exposed to the stromal compartment but is able to digest proteins exposed to the intermembrane space between the two envelope membranes. Previous reports indicating that trypsin is able to degrade Tic110 were influenced by incomplete quenching of protease activity.When trypsin is not sufficiently quenched, it is able to digest Tic110, but only after chloroplasts have been ruptured. It is therefore necessary to employ adequate quenching protocols, such as the one reported here, whenever trypsin is utilized as an analytical tool. Based on a stromal localization for the majority of Tic110, we propose that this protein may be involved in the recruitment of stromal factors, possibly molecular chaperones, to the translocation apparatus during protein import.